Internally prestressed reinforcement rod



1 9 1970 I J. J. RIEVE 3,516,211

INTERNALLY PRES'IRESSED REINFORCEMENT ROD Filed Jan. 18, 1968 z Sheets-Sheet 1 lnventar: JOHA u d. RAE vs b72 ,FQMZMW 1 1 June 23, 1970 J- J. RIEVE INTE RNALLY rnns'rnnssm REINFORCEMENT ROD Filed Jan. 18, 1968 2 Sheets-Sheet 2 up Hun".

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Inventor:

JOHA/WV J Rial s ATTYJT United States Patent 3,516,211 INTERNALLY PRESTRESSED REINFORCEMENT ROD Johann Jacob Rieve, Dusseldorf, Germany, assignor to Betonnnd Monierbau AG, Dusseldorf, Germany, a

l'IIl Filed Jan. 18, 1968, Ser. No. 698,928 Claims priority, application Germany, Jan. 20, 1967, B 90,818; May 6, 1967, B 92,384 Int. Cl. E04c 3/10, 5/08 US. Cl. 52-230 Claims ABSTRACT OF THE DISCLOSURE This invention provides an internally prestressed reinforcement rod for prestressed concrete consisting of a core serving as a push rod and peripheral sections. The core may be in the shape of a hexagon, a circle, or a rectangle, and the peripheral sections are shaped to surround and conform to said core leaving only slight gaps between themselves and said core. At least one of the gaps between the peripheral sections may be V-shaped. A clamp unit is provided to act as an anchoring means for the prestressed reinforcement rod after it has been prestressed by a push on the core and a simultaneous pull on the peripheral sections, which clamp unit holds the reinforcement rod in its internally prestressed condition until its removal after the complete installation of this reinforcement rod, whereupon the internal stress becomes a stress in the concrete.

BACKGROUND OF THE INVENTION This invention relates to an internally prestressed reinforcement rod for prestressed concrete.

Such reinforcement rods are prestressed in the workshop and then delivered together with their anchoring means to the construction site. When a great quantity of reinforcement rods is needed, the prestressing can be done at the construction site itself. After their instal ation and the hardening of the concrete, the anchoring means which holds the rods in their prestressed condition is loosened so that the internal stress in the reinforcement rod becomes a stress in the concrete. Finally, the core is withdrawn and the hollow space resulting from this operation is filled up by injecting concrete ooze therein.

Prestressed reinforcement rods having a core in the form of a link-articulated chain so that the prestressed reinforcement rod can bow on installation are known in the art.

With these reinforcement rods, the core or push member lies in a thin sheet-metal tube. The peripheral sections consist of tension wires which are wound around this sheet-metal tube in two opposing oblique directions. The sheet-metal tube is necessary to prevent the core from getting embedded in concrete if any of this concrete passes through the gaps between the tension wires. Such reinforcement rods are relatively expensive to produce. Moreover, recovering the core or push members is troublesome and expensive.

The same is true for another known reinforcement rod where a sheet-metal is wound around a bar-shaped core or push member. Stranded wires, which are wound like a cable around this sheet-metal strip to form peripheral members and are anchored at their ends after being stressed.

In order to eliminate the necessity of a sheet-metal tube or a sheet-metal winding, it has been further suggested (German Utility Model-1,799,425) to use a round steel rod as the core or push rod around which a plurality of tension wires with a circular cross section are so tightly grouped that the concrete cannot penetrate to the core.

3,516,211 Patented June 23, 1970 However, also such reinforcement rods have not proved satisfactory in practice. The reason for this is that it is very diflicult to maintain the plurality of tension wires of the reinforcement rod in alignment, particularly when this rod bows, which alignment is necessary to prevent the concrete from penetrating between the tension wires to the inside and thus making it impossible to withdraw the core afterwards. A further disadvantage of this known reinforcement rod is that part of the tension wires lie tightly on the core when they are stressed thereby making it considerably more difficult to withdraw this member later on.

SUMMARY OF THE INVENTION It is the object of the present invention to avoid the above-mentioned disadvantages and to provide a novel method of prestressing concrete and an interna ly prestressed reinforcement rod therefor, which rod is relatively inexpensive to manufacture due to its particularly simple construction. In addition, the reinforcement rod should be made so that the core is not in danger of getting embedded in concrete and so that this core is easy to withdraw after the reinforcement rod is embedded in the concrete and the end anchorings were loosened, even when the reinforcement rod is bowed.

To attain this object, the present invention provides a method of prestressing concrete and an internally prestressed reinforcement rod for the prestressed concrete, which comprises a core serving as a push rod, and at least two peripheral sections enclosing said core and having insides shaped to conform to the surface of the core, said peripheral sections being adapted to serve in the prestressing of the reinforcement rod before its installation by being pulled as said core is pushed.

This design makes it possible to dispense with the hollow tube or the mounting of a great number of round tension wires which jointly have the function of a hollow tube, since it is possible to enclose the core with only two peripheral sections. With only two peripheral sections, a slight clearance is advantageously left between the peripheral sections and the core, which slight clearance facilitates the later withdrawal of the core. In this arrangement the peripheral sections support each other on their edges.

It is advantageous to form these peripheral sections as half split rings when the core has a circular cross section.

Instead of this, the peripheral sections may be of U-shaped cross section while the core has a substantially quadratic cross section. From a technical, manufacturers point of view, this solution particularly lends itself to the use of peripheral sections formed from rolled steel.

According to another characteristic feature of the invention, at least one of the longitudinally extending gaps between the peripheral sections is V-shaped which prevents these peripheral sections from moving laterally relative to each other. Moreover, such a V-shaped gap largely prevents concrete ooze from penetrating through the gap between the peripheral sections into the clearance between them and the core.

According to a further embodiment of the invention, the striven-for advantages may be attained in that the core has a quadratic cross section, and four flat peripheral sections are provided which enclose said core. These peripheral sections may have a right-angle cross section and thus the same shape. Instead of this, they can be shaped like strips or plates, each peripheral section covering one flat side of the shaped core.

According to a still further embodiment of the invention collars spaced along and encircling the reinforcement rod may be provided for maintaining this reinforcement rod in the position necessary to keep concrete ooze from penetrating to the core.

According to a further characteristic feature of the invention; the reinforcement rod may-be provided with at least one anchor plate which is held on the peripheral sections by at least one key or by some other means. These anchor plates can be embedded in the concrete with the reinforcement rod when it is installed. It has proved advantageous to use such anchor plates on the outer ends of reinforcement rods to transmit the stressing force to the outside of the structural member in which it is embedded.

BRIEF DESCRIPTION OF THE DRAWINGS Several embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, .in which:

FIG. 1 is a cross section through a reinforcement rod according to the invention with two U-shaped peripheral sections and a hexagonal core;

FIG. 2 is a cross section through a second embodiment of areinforcement rod with two semi-circular peripheral sections and a circular core;

FIG. 3 is a cross section through a third embodiment of a reinforcement rod with a quadratic core and four flat bar-shaped peripheral sections;

FIG. 4 is a longitudinal section through a stressing press and an anchoring with one end of a reinforcement rod clamped therein;

FIG. 5 is a longitudinal section on the line V-V of FIG. 4, and

FIG. 6 is a longitudinal section through a reinforcement rod embedded with its anchoring means in concrete.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a reinforcement rod 1 which consists of a push rod or core 2 with a hexagonal cross section, and two peripheral sections 3 and 4 with U-shaped cross sections. The inside of the two peripheral sections 3 and 4 is shaped to conform to the surface of the core 2 so that a slight clearance exists between the two peripheral sections 3 and 4 on the one hand and the core '2 on the other hand. Even supposing a bowing in the reinforcement rod 1, this clearance permits the core 2 to be withdrawn from between the peripheral sections 3 and 4 after the concreting operation.

' This clearance also exists in the reinforcement rod 1 shown in FIG. 2. Here, the peripheral sections 3 and 4 consist of semi-circular bodies and the core 2 hasa circular cross section. A further difference between this reinforcement rod 1 of FIG. 2 and the reinforcement rod 1 of FIG. 1 is that the longitudinally extending gap between the two peripheral sections 3 and 4 shaped like semicircles has a substantially V-shaped cross section for preventing concrete ooze from penetrating into the annular clearance between the core 2 and the peripheral sections 3 and 4 A further advantage of this substantially V shaped gap is that it prevents the two peripheral sections 3 and 4 from moving laterally relative to each other.

' The reinforcement rod 1 according to FIG. 3 has a core 2 with a quadratic cross section and four peripheral sections 3 and 4 which are formed as fiat bars. The two peripheral sections 3 have the same shape, as do the two peripheral sections 4 As already mentioned, the reinforcement rod is prestressed before being installed, taking the reinforcement rod 1 of FIG. 1 as an example although the following process is the same for the reinforcement rods 1 and 1 A clamp unit 8 shown in FIGS. 4 and 5 is provided for this purpose. This clamp unit 8 consists of two clamp plates 9 and 10 between which the peripheral sections 3 and 4 are clamped by means of bolts 11 and keys 12 (FIG. 5). In their rear portions the clamp plates 9 and 10 are provided with recesses 13 and 14 in which hooks 15 and 16, respectively, of two stressing arms 17 can engage. The stressing arms 17 form a componentpart of a 18 the forward end 'of which extends between the clamp plates 9 and 14) to a guide body 19. This guide body 19 is provided on its forward end face facing the reinforcement rod 1 with a recess 20 in which the rear end of the core 2 engages.

In order to prestress a reinforcement rod 1, the clamp plates 9 and 10 are screwed tightly together on the peripheral sections 3 and 4, then the clamp unit 8 is drawn toward the left in FIGS. 4 and 5 by means of the stressing arms 17 which action forces the pressing rod 18 against the guide body 19 and therefore against the core 2 thus moving it slightly relative to the peripheral sections 3 and 4 and thereby putting a stress in the reinforcement rod 1.

Once the required magnitude of prestressing is attained in the arrangement seen in FIGS. 4 and "5, splines 23 and 24 are inserted between the guide body 19 and walls 21 and 22 of the clamp plates 9 and 10 for maintaining the prestressing after the stressing arms 17 and the pressing rod 18 have been loosened. Subsequently, the now prestressed reinforcement rod 1 is delivered to the construction site with its anchoring consisting of the clamp plates 9 and 10, the bolts 11, the keys 12, the guid body 19, and the splines 23 and 24.

In addition to these previously mentioned parts, the reinforcement rod 1 is provided with two anchor plates 30 and 31 (FIG. 6) which are held by keys 32 on the end portions of the peripheral sections 3 and 4. Collars 33 spaced at a distance from one another are arranged between the anchor plates 30 and 31 for holding the peripheral sections 3 and 4 together in the desired position. As shown in FIG. 6, the anchor plates 30 and 31, the keys 32, and the collars 33 are all embedded in concrete with the end of the reinforcement member 1 which end can be provided with an air vent 34.

After the concrete has hardened, the anchoring on the end of the reinforcement rod 1 can be removed by driving out the splines 23 and 24, loosening the bolts 11, and removing the keys 12 whereupon the pull in the reinforce ment 1 becomes a push acting on the structure.

As can be seen in FIG. 6, an abutment 35 is Welded inside one end of the reinforcement rod 1 on the peripheral sections 3 and 4 behind the end of the core 2. The core 2 is braced against this abutment 35 when the reinforcement rod 1 is only prestressed from one end which is less troublesome than prestressing it from both ends and which is possible with a reinforcement rod designed as proposed by the invention since practically no friction between the core 2 and the peripheral sections 3 and 4 need be taken into consideration.

After removing the previously mentioned anchoring from the end of the reinforcement rod, the portion protruding from the structure is removed, for example by cutting it off with an oxygen-hydrogen torch. Either before or after the cutting operation the core 2 is withdrawn from the structural member and concrete is injected into the hollow space formed by this withdrawal, the air contained therein escaping through the air vent 34.

It has been found that the push rod or core can also be used in another manner, i.e. as a stressing member in order to increase the economy of prestressing.

According to a development of the invention this can be achieved, when the push rod or core after the transmission of the stressing force from the peripheral sections to the concrete will not be withdrawn from the structural member, but will be prestressed itself, the pressing force being directly transmitted into the structural member. A final anchoring of the prestressed push rod or core can then be effected in a known manner by means of an anchoring plate and a nut. Finally the holloW space between the'push rod or core and the peripheral sections is filled up by injecting concrete ooze thereinto.

The advantages of this procedure are that it is not necessary to withdraw the push rod or core that is especially difficult when the stressing member has lost its straight configuration. Besides, the push rods or cores need not be transported back.

Furthermore the prestressing of the concrete will be very much increased while the costs are kept low.

The invention may be embodied in other specific forms without departing from the spirit or esssential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changed which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. A reinforcement rod assembly for prestressing concrete comprising,

(a) a core member forming a profiled push rod means,

(b) at least two peripheral shell members substantially surrounding said core member, and

(c) means providing an abutment for said rod means to push against the shell members in a longitudinal direction of said assembly,

(d) said shell members being in spaced relationship with respect to said core member to form an open clearance gap therebetween,

(e) each said shell member having edges juxtaposed an adjacent shell member to provide support to each other.

2. A reinforcement rod assembly as defined in claim 1 wherein said juxtaposed edges are in spaced relationship to form open gaps therebetween.

3. A reinforcement rod assembly as defined in claim 1 wherein said juxtaposed edges have corresponding sur face shapes to prevent lateral movement of said peripheral shell members with respect to each other.

4. A reinforcement rod assembly as defined in claim 3 wherein said corresponding surface shapes form V- shaped open gaps therebetween.

5. A reinforcement rod assembly as defined in claim 1 wherein said assembly includes collar means which encircle said peripheral shell members to maintain the relationship between the shell members to prevent concrete from penetrating the assembly to the core member.

6. A reinforcement rod assembly as defined in claim 1 wherein said assembly includes at least one key means to hold at least one anchor plate means on said peripheral shell members.

7. A reinforcement rod assembly as defined in claim 2 wherein said peripheral shell members comprise rolled steel.

8. A reinforced rod assembly as defined in claim 7 wherein said peripheral shell members have a U-shaped or a half split ring shaped cross-section.

9. A reinforcement rod assembly as defined in claim 2 wherein said core member has a quadratic cross-section and there are four flat peripheral shell members surrounding said core member.

10. A reinforcement rod assembly as defined in claim 2 wherein said assembly includes means to clamp the ends of said peripheral shell members,

means to brace splines for transmitting a pull force to the shell members, and

means to produce a push force on said core member simultaneously with said pull force.

References Cited UNITED STATES PATENTS 2,328,033 8/1943 Schorer 52230 2,378,584 6/1945 SchOrer 52-230 2,449,276 9/1948 Chalos 52230 2,737,802 3/1956 Bakker 52-230 2,963,273 12/1960 Lane 52223 X 3,167,882 2/1965 Abbott 52-230 X ALFRED C. PERHAM, Primary Examiner US. Cl. X.R. 5-2730 

